There is known a vehicle brake fluid pressure controller which performs, to suppress wheel locking, antilock brake (ABS) control in which the state of a wheel being likely to lock is judged on the basis of wheel velocity and the brake fluid pressure corresponding to the wheel being likely to lock is decreased. Also, for example, JP-H11-180281-A discloses a vehicle brake fluid pressure controller which performs braking force distribution control in which the brake fluid pressure on the side of the rear wheels is limited depending on the depressing speed of the brake pedal.
However, in the case that sudden braking is performed, the load of a vehicle is apt to be applied to the front wheels thereof, and the hydraulic pressure in the front brakes rises at the time when pressure decrease (ABS) control is started. Hence, when the front wheels are likely to lock after sudden braking, a pressure decrease amount until dissolving the locking state of the wheels increases. In addition, after this pressure decrease, the pressure is apt to increase suddenly. As a result, significantly large sudden pressure decrease and sudden pressure increase are repeated at the initial stage of the ABS control. Hence, the braking operation becomes unstable as such situation corresponds to a so-called overshooting situation (largely exceeding the target value of control) in the control engineering. When the hydraulic pressure balance between the front and rear wheels is adjusted by decreasing the hydraulic pressure of the rear wheels as in JP-H11-180281-A, the ratio of using the braking force of the front wheels is relatively large. Thus, such situation becomes more serious.
In addition, JP-2009-023468-A discloses a vehicle brake fluid pressure controller which performs sudden pressure increase control for increasing pressure at a steep inclination, and thereafter, performs gradual pressure increase control for increasing pressure at a gentle inclination is performed. In JP-2009-023468-A, a normally-open proportional solenoid valve is used. Hence, sudden pressure increase control is performed by steeply lowering the control current to the set break point current value, and gradual pressure increase control is performed by gently lowering the control current from the set break point current value.
In other words, this technology sets respective indication hydraulic pressures (target of the hydraulic pressure inside a wheel cylinder) for a period of controlling the hydraulic pressure with a steep inclination and for a period of controlling the hydraulic pressure with a gentle inclination.
However, even if the indication hydraulic pressure is raised at the steep inclination to perform the sudden pressure increase control, the actual hydraulic pressure may not respond as specified by the indication hydraulic pressure in some cases, and the inclination of the pressure increase may become slightly gentler than the inclination of the indication hydraulic pressure. Thus, the sudden pressure increase control in which the actual hydraulic pressure can be increased more quickly is desired.